DPM (was Proper Mixture)

[Darrell Norquay]

At 10:37 AM 8/1/96 -0500, you wrote:


>Summary:  the inputs are differential, but cannot go past either
>voltage rail (no problem -- the O2 sensor has one lead at ~ 0 and the
>other never exceeds ~ 1 volt).  The ICL-7106 is spec'ed at 15 volts
>max, so the DPM "should" be OK being powered directly from the car system
>and should not have any problems with noise being induced into the
>sensor readings (certainly not enough so's one would notice).

The automotive electrical system can have voltages as high as 16-18 volts
steady state, and transient voltages a LOT higher than that.  In my
experience with DPM's, the 9V powered models artificially produce a ground
halfway between the supply rails, so you cannot connect INLO to the - supply
lead.  Nor can you measure the voltage of the battery with the meter that it
is powering, for the same reasons.  Better off just to stick with the battery...



regards
dn
dnorquay at awinc.com